Concentration of ores



May 6, 1941.

LE RoY E. scHlFFMAN Erm.

CONCENTRATION OF ORES Fild Aug. 15, 1938 3 Sheets-Sheet. 1

May 6, 1941.

3 Sheets-Sheet 2 BMW INVENTORS l B Y ATTORNEYS May s, 1941*. A

LE ROY E. SCHIFFMAN 4EI'AL CONCENTRATION oF oREs Filed Aug. 15, 1938' 3Sheets-Sheet 3 INVENTORS idw@ wlw# M M www BY M m, VMM

Y ATTORNEYS' Patented May 6, 1.941

CONCENTRATION F ORES Le Roy Edgar Schiffman, Claude Sims Lawson, andJoseph Thomas Blakemore, Birmingham,

Ala.

Application August 1s, 193s, serial No. 224.694

Claims.

This invention relates to the concentration of low grade iron ores, suchas 10W grade oxide andv carbonate ores, etc., and comprises an improvedmethod of treating such low grade iron ores by a combined roasting andgrinding treatment, and particularly a combined reducing and grindingtreatment, followed by separation ofthe treated ore, and particularlymagnetic separation, to produce a high grade iron ore or concentrate.The invention includes various steps and features of the process, asWell as combinations thereof, as will appear from the following moredetailed description. The invention also includes an improved apparatusand equipment for use in carrying out the process.

The invention is of more or less general application to the treatment oflow grade oxidized iron ores, such as oxide and carbonate ores, etc.

It is particularly applicable to the treatment cf low grade iron oxideores, for example, oolitic hematite ores, which 4are of too low grade tobe used in their present state, in order to produce therefrom a highergrade ore or concentrate adapted for use in place of the present highergrades of ore, the supply of which is limited.

It has been proposed to roast low grade hematite ores in preparation formagnetic separation, but it has been found necessary to grind the ore,after roasting, to a point where the gangue material is freed from themineral bearing portion of the ore in order to effect an efficientseparation.A With ores in which the mineral and the gangue Aareintimately mixed,4 this has heretofore vrequired very ne grinding.Oolitic hematite ores, for example, ordinarily require grinding to atleast minus 100 mesh and preferably minus 200 mesh for good separation.

We have found that by subjecting such low grade hematite ores to acombined roastinggrinding treatment, and particularly to a comb-inedreducing-grinding treatment, an eflicient separation can be effectedwithout such ne grinding, and with other advantages, such as thosehereafter pointed out. Using the combination roasting-grinding method ofthe present invention, we have made effective separation with 80% of thematerial plus 60 mesh in.

size. We have also taken that portion of the treated product that wasminus mesh and plus 40 mesh and obtained a better separation than wewere able to obtain at minus 80 nesh with material separately roastedand ground before treatment.

According to the present invention, the low grade iron ore, afterpreliminary crushing, ls

subjected to roasting While grinding at a high temperature; and We nd itof particular advantage to subject the ore to a reducing atmospherewhile grinding at a high temperature. Apparently we secure a verydesirable type of breakage and grinding by combining grinding with theroasting, or roasting and reducing, treatment. It is advantageous, insome cases, to subject the 'ore alternately to reduction and tooxidation while grinding at high temperature.

The combined grinding and roasting of the low grade ores presentsvarious advantages, including the following: Due to the grinding actionwhile the ore is hot, or while hot and while being subject to reduction,the desirable mineral bearing portion of the ore is better separatedfrom the gangue and other desirable portions, the

cleavage of the particles being broken apparently along the separatingboundaries between the iron oxides and the siliceous matter; thedesirable portion of the ore is better separated fromf the gangue andother undesirable portions so that subsequent separation, such asmagnetic separation, can be more effectively made; the grinding appearsto be selective, the impurities in general being less reduced in sizethan the desirable portion of the ore; effective magnetic separation canbe made with larger siz'e ore particles than by the prior methods; lessgrinding is required to effect separation with resulting economy inreduction of grinding costs and less need of agglomeration of theconcentrate before further treatment; the magnetic portion of thematerial treated appears to be made more highly magnetic than inordinary roasting; the need of less grinding allows retention of morelime in the concentrate when separating oolitic hematite ores so thatthese ores can be concentrated with less` loss of lime than in othermethods;

fand the concentration of low grade oolitic hemaapplies: By grinding theore whilehot, the friability of the different materials constituting the'ore is probably different from that in grinding cold material, probablycausing a different type of breakage in the grinding process; some waterof crystallization is driven off causing an internal f force to act uponthe material, or to weaken the treatment.

grinder.

structure of the material, at the same time that it is being subjectedto the external force of grinding; some carbon dioxide from carbonatematerial being driven o causes an internal force to act upon ythematerial, or to weaken the structure of the material, at the same timethat it is being subjected to the external force of grinding. Bygrinding the ore while hot and while subjected to a reducing atmosphere,additional influences are exerted in addition to those referred to inconnection with grinding the ore While hot; the oxygen being taken fromthe mineral portion of the ore, due to the reducing atmosphere whichconverts hematite to magnetite, apparently either causing an internalforce to act upon the material or to weaken the structure of thematerial, at the same time that it is being subjected to the vexternalforce of grinding. When the ore is ground hot and while subjected toalternately reducing and oxidizing atmospheres there is, in addition tothe actions above mentioned, a further action, namely, during thesubjection to an oxidizing atmosphere after a subjection to a reducingrvatmosphere oxygen is added to the mineral portion of the ore causing aninternal force to act upon the material at the same time that it isbeing subjected to the external force of grinding. Whether thesetheoretical explanations furnish the real reason for the improvedresults obtained, we have nevertheless obtained improved results,

of the character hereinbefore mentioned, by combining the grinding ofthe ore with the roasting, and other treatments.

In carrying out the presentprocess the low grade ore is first .crushedto a suitable size in a suitable crushing equipment, e. g., minus 3Ainch or minus V2 inch. The crushed ore can then be supplied to theapparatus by which the combined roasting and grinding is accomplished.The crushed ore is advantageously preheated before subjecting it to thecombined roasting-grinding Thisl results in conservation of fuel,enables the capacity of the roaster-grinder to be increased, and enablesbettery control of the roaster temperature. Preheating may be carriedout in separate equipment or in equipment combined with theroasting-grinding equipment. The temperature attained in the preheatingtreatment may approach that used in the roaster.. grinder or may evenexceed that in the roaster- The preheating can advantageously beaccomplished with the use of the hot gases escaping from theroaster-grinder, for example, by combustion of the reducing gasesescaping from the reducing-.grinding operation, withadditional fuel ifrequired, for example, using additional fuel such as coal, coke, fueloil, producer gas, coke oven gas, natural gas, or other similarcombustible material.

The low grade ore, preliminarily crushed, and

- advantageously preheated, it is next subjected to 1during the combinedroasting-grinding treatment will vary somewhat with the ore and itscomposition. In general the temperatures will be above supplied invarious ways.

500 and not above 2000 F. and more advantageously within the range of9001500 F. with low grade iron ores of the character referred to. It isdesirable to hold the temperature below that at which sintering takesplace, which temperature will vary with different ores and with thecharacter of the gangue present. With the oolitic hernatite ores we haveinvestigated, no appreciable sintering has occurred below 1500 F., andusually temperatures above 2000 F. were required to show any indicationof sintering.

With such low grade iron ores good results have been obtained attemperatures somewhat below 1000 F. in the combined reducing-grindingoperation but more prolonged exposure to the reducing atmosphere isrequired, and the type of breakage secured in this combined operation is'apparently not as good as at somewhat higher temperatures. The use ofhigher temperatures reduces the time of exposure to the reducingatmosphere that is required and improves the type of grinding, but it isdesirable, as above pointed out,-to hold the temperature below thesintering point, and also to keep it low enough to protect the lining ofthe grinding mill and the grinding media. Temperatures within the rangeof 1000 F. to 1500 F'. appear to be the most desirable. The timerequired for the combined reducinggrinding operation will vary somewhatwith the temperature and with the reducing medium used. When using arotating ball mill with crushed ore preheated to about 1 050 F. and withcoke oven gas supplied as the reducing atmosphere, we have found aperiod of treatment of twenty-five minutes sumcient, with increase oftemperature to about1200 F.

'I'he reducing medium or atmosphere for the combined reducing-grindingoperation can be In general, a reducing atmosphere should be maintained,but a large excess of reducing gas does not appear necessary. We haveobtained good results with a fully reducing atmosphere with but verylittle neutral gases present. We have obtained good results with the useof coke oven gas to furnish the reducing atmosphere but the reducingatmosphere may be otherwise obtained, for example, by the use 0f blastfurnace gas, natural gas, vaporized oil, etc. 4

The heating of the ore during the combined roasting-grinding operationcan be accomplished in various Ways. The preheating of the crushed orereduces the heat required during this combined operation. Electricalheating can be employed when -available at a suiiciently low cost. Theheating can be accomplished by burning fuel and using the products ofcombustion and this can be accomplished Within the apparatus byincomplete combustion which gives a reducing at.- mosphere. Coal can beadmixed with the ore in the roaster-grinder with resulting driving oi ofvolatile material which furnishes a highly reducing gas, and by burningthe coal with insuiiicient air heat is supplied together with reducinggases; or the heating and reducing gases may be separately supplied tothe apparatus in which the combined roasting and grindingoperationis-carried out.

In some cases it is advantageous to subject the ore alternately to areducing and to an oxidizing atmosphere, particularly in the case ofrefractory ores where a single reducing-grinding treatment does notsuiciently prepare the ore forfurther treatment. By following thereducing treatment with anoxidizing treatment, both in combination withthe grinding treatment, the ore will be first reduced and then oxidized,and these operations will be repeated, if necessary. The oxidizingatmosphere will re-oxidize the reduced ore and it may then be subjectedto a further reducing-grinding treatment to accomplish furtheradvantageous results from this combined operationl and to leave the orein a reduced state where, for example, a magnetic ore is desired forsubsequent. magnetic separation.

In order to avoid re-oxidizing of the ground and reduced ore, this oreshould be protected from the atmosphere while hot. Cooling of the orecan readily be accomplished by a limited quenching with water in justsufiicient quantity to quickly reduce the temperature to somewhat aboveatmospheric Without saturating with water. If the treated ore is to besubjected to wet separation, the ore from the combined roastinggrindingtreatment can be discharged into water at this point. The hot ore canalso be cooled, Without quenching, in apparatus in which it is protectedfrom atmospheric oxidation.

The reduction treatment to which the low grade iron ores are subjectedreadily reduces the red iron oxide or hematite to magnetic iron oxide ormagnetite; and the combined reducing and grinding treatment yleaves thereduced ground material in a form particularly well adapted forsubsequent treatment by magnetic separation, or by magnetic separationcombined with sizing or screening and other separation treatment. Wherethe ore is to be subjected to magnetic separation, the reduced oresshould be cooled in a manner such as to substantially preventre-oxidation. Where wet separation, or separation other than magneticseparation, is to be used, this precaution may be unnecessary.

It is one of the advantages of the process of the present invention thatne grinding to a uniform small size is not necessary,v and larger sizeparticles can be effectively separated than where the grinding operationfollows the roasting and cooling of the ore. In general it will bedesirable to remove from the product particles larger I i than 20 meshand to return them to the grinder .for re-Working; but we have secured ahigh grade concentrate with good iron recovery from the product of thecombined reducing and grinding treatment by subjecting run of millmaterial to magnetic separation with no sizing or re-working of thematerial.

It is more advantageous, however, because of the varying sizes of theparticles, to subject the product from the master-grinder to a sizingtreatment, after for example, to sizing by screens or by hydraulicclassiersor both, to obtain products of various sizes which can beseparately subjected to magnetic separation. The concentrate productfrom the larger sizes may, in some cases, be advantageou'sly returned tothe roaster-grinder for reworking, if desired, or may be treated as a-nal concentrate, while the rejected material is discarded'.

We have found that by sizing the material before separation, a moreeificient separation can be obtained on the sized material, and better,efiiciency secured from each separator by presenting to it a moreuniformly sized product.

We have also found it of. advantage to use magnetic separators with themagnet strength so adjusted as to remove that portion ot thematei-iaiwhich it is desired to remove allowing the less magnetic material to bediscarded, or subit has been cooled or quenched,

to a second setof separators to lessen the loss in the tailings. 'Iheconcentrate from the second set of separators may either be sent directto the final concentrate or treated as middlings for further re-working,while discarding the rejected material.

The invention will be further illustrated and described in connectionwith the accompanying drawings which are somewhat diagrammatic incharacter and illustrate apparatus adapted for carrying out theroasting-grinding operation in various ways, and a flow sheet showingthe combination of the various steps of the process including magneticseparation. While the product of the roasting grinding treatment isamenable to other methods of separation, the invention will be moreparticularly described in combination with magnetic separation, withindication of the advantages thereby obtainable.

In the accompanying drawings:

Fig. 1 shows one form of apparatus including the preheater and combinedroaster-grinder;

Fig. 2 shows a modified construction and arrangement of the preheaterand combined roast- 'er-grinder;

Fig. 3 shows a paratus;

Fig. '4 shows another modified form of apparatus; and

F.ig. 5 shows a iiow sheet of the complete opation from the crushing ofthe ore to the nal magnetic separation for the production of finalconcentrate.

'I'he apparatus of Figs. 1 to 4 includes preheating ararngements ofdifferent kinds and somewhat different types of constructions andarrangements of the roaster-grinder. In Figs. 1, 2 and 4 the preheateris separate from the roaster-grinder, while in Fig. 3 the preheater is apart further modified form of apof the same equipment.

In Fig. 1 the master-grinder consists of a cylindrical cast iron liningor shell I surrounded by insulation 2 and an outer jacket or shell 3.The cylinder is slightly inclined from the horizontal, has anges 4mounted on rollers 5 and is arranged to be rotated by means of the gear6. Grinding media (not shown) such, for example, as iron balls, are tobe used in this rotating cylinder. One end of the cylinder is shown asclosed by a plate 1 with an opening 8 in it for a gas burner (notshown). The other end is partly closed by plate 9 to retain the grindingmedia and having an opening I0 above it to permit the introduction ofore and the escape of gases, This end is inserted into a brick preheaterI2 which contains sloping shelves I3 over which the ore is fed and withopenings I4 which in operation will be closed except for thelinsertionofy mechanical devices for insuring the feed of the ore crimechanicallydrivenrams (not shown)l for aiding in the regulated feed of the ore.

At the bottom ot the preheater is a chamber I5 which may serve as asupplementary combustion chamber lfor supplying additional heat. Anairport I6 permits'fresh air to be introduced, for example, .for thevcombustion of reducing gases` coming from the master-grinder and toprovide additional heat for the preheating operation; and

air may also enterat |6a between the cylinder and preheater.

The burner end of the cylinder has openings I6 around its circumferenceto permit discharge of the roasted ore,- a stationary ring I1 beingshown for closing the outer openings except at the bottom where openings|8 are provided to permit escape of' the ore therethrough. Dischargepipes or receptacle (notv shown) Will be arranged to receive thedischarged ore and for protecting it against re-oxidation until cooledor quenched.

The apparatus of Fig. 2 has a separate preheater 20 and roaster-grinder2|, both being rotatable cylinders, slightly inclined, and theconstruction of which is generally similar to that of the cylinder ofFig. 1. The cylinder 20 has ar series of inletopenings 22 near one end,with a stationary ring 23 closing the openings, except at the top whereore is introduced through the hopper 24. A similar means for dischargingore is provided at the other end of the cylinder' through openings 25.The discharge end 'of the cylinder isshown as provided with an opening26 connected with flues 21 leading from a combustion chamber forintroducing hot gases, or combustible gases and air, for preheating theore. The. other end of the preheater has an opening 35 connected with apipe 36 leading, e, g., to a cyclone dust connector (not shown) andthence to a stack.

'I'he preheated ore is discharged through the openings 25 and openingsin the ring 28 into the hopper 29 and thence through similar openings 30into the master-'grinder cylinder 2|. The outlet end of this cylinderhas similar discharge openings 3| to the openings I6 shownin Fig. 1, Aninlet 32 near the discharge end of the cylinder provides for introducingreducing gases, or of products of combustion with excess of reducinggases, and the other end of the cylinder has an outlet opening 33 forthe gases connected with the pipe 34 leading, e.- g., to a cyclone dustcollector (not shown). It will be understood that theY cylinders 20 and2| are rotatable, for example, in a manner similar to the rotation ofthe roaster-grinder cylinder of Fig. 1, and that the master-grinder 2|will contain balls or other grinding elements.

The apparatus of Fig. 3 shows a single cvlinder having a preheatingsection and a roastergrinder section. In general. construction it issimilar to the cylinder of Fig. l and corresponding parts are indicatedby the same reference numerals, and provision is made for feeding theore to the preheater through a hopper 31 arranged similar to the hopper24 of Fig. 2. Centrally arranged in the cylinder is a perforated castironplate 38 having openings to permit the ore to pass therethrough butfor preventing the Iballs or vgrinding media from passing therethrough.This cylinder also has aseries of air- "ports 39 surrounded bystationary `air pipe 48 through which supplementary air canbe introducedfor combustion of the reducing gases coming from the master-grindersection `to aid in preheating the ore. These air inlet ports 39 extend asumcient distance-into the Acylinder to preventfore from entering themfrom the cylinder. Similar ports^ not shown) can b e used for supplyingadditional fuel or additional hot gases and a surrounding hollowstationary ring closely fitting the shell. The end of the preheatersection of the cylinder has an opening 4| extending into the stack 42.

'I'he apparatus of Fig. 4 corresponds for the most part to theconstruction of the apparatus of Figs. 1 and 3 and corresponding partsare indicated by the .same reference numerals. In addition the apparatusof Fig. 4 has supplementary means for introducing air at an intermediateportion of the cylinder thru an airport 43 connected with"air pipes 44in a perforated cast iron plate 45 which has openings to permit by hotproducts of combustion which may be separately introduced, as in Fig. 2,or which may be heated by combustion of the reducing gases coming fromthe roaster-grinder, with supplemental combustion thereof fby theseparately introduced air, as in Figs. 1, 3 and 4. The preheated o reenters the roaster-grinder section of the apparatus and is theresubjected to a combined grinding and reducing treatment by thesimultaneous action of the grinding media and of the reducing gases. Thepreheated ore may be further heated by incomplete combus- ,tion in theroaster-grinder section of the apparatus. In Fig. 4 the introduction ofair intermittently into .a part of the master-grinder permits ofobtaining oxidizing conditions and reducing conditions alternately andintermittently during-part of the grinding operation, and

subsequently obtaining reducing conditions duri ing the final stage ofthe grinding operation.

In the operation of all of the di'erent arrangements of apparatusillustrated provision is made for preheating the ore before it issubjected to the roasting-grinding operation, and the preheated ore isthen subjected to a combined roasting and grinding operation whichincludes, in all of the instances illustrated, a combined reducing vandgrinding treatment, and which may (be combined, as in Fig. 4, with apreceding alternate oxidizing and reducing treatment during part of thegrinding operation( In the operation of all of these forms of apparatusthe ore discharged will be vquenched or cooled' where re-oxidation is tobe prevented this subsequent part of the apparatus for this quenching or`cooling treatment not being illustrated in the drawing.

It will be evident that therate at which the ore is fed to the apparatusand is passed therethrough .can be regulated, depending upon the size ofthe cylinder, its dimensions, the rate of rotation, ete. to obtain thedesired degree of grinding combined with reduction, these operationstaking place simultaneously. A preferred speed 0f rotation of thecylinders is that ordinarily used in mill practice 'where the balls,pebbles, or rods are made to cascade or fall onto the ore. The grindingof the ore and the agitation of the ore by the rotation of the cylindercontinually subjects fresh portions of the ore to the grinding andreducing treatment. The preferred temperature range at which theroasting and grinding is carried out isaround 1000 to 1500, F. and

wehave. obtained good results at temperatures ow'sheet of the variousoperations including-` the preliminary crushing, preheating,roastergrinder treatment, quenching, sizing and magnetic separation. Thesizing operation illus-` trated includes screening and hydraulicclassification.

According to the operations illustrated in the ow sheet the material isfed to the crusher of gyratory or other type for crushing the ore, e.g., to minus 1/2 inch. The crushed ore then passes through the preheaterwhich may, for example, [be a preheater such as illustrated in Figs. 1kto 4. Provision is made for returning certain of the materials fromsubsequent magnetic separation for further treatment. 1

From the preheater the material passes to the combined roaster andgrinder where it is subjected to simultaneous grinding and roasting. Inthe apparatus of Fig. 4, by admitting or shutting oil air at theintermediate stage of the roaster-grinder, the atmosphere in a. portionof the cylinder can be made oxidizing, and by closing off the gases theatmosphere can be made reducing, thus providing for one or morealternate oxidizing andreducing treatments when desired. The i'lnalportion of the grinding operation in the apparatus of Fig. 4, as well asthe grinding operations in the apparatus of Figs. 1 to 3, is made underreducing conditions so that thinal reduced product discharged will bemagneI c.

In the ow sheet the material from the roaster-grinder is subjected toquenching, e. g., with a limited amount of Water or by cooling undernon-oxidizing conditions, and is then passed through 10 mesh and 20 meshscreens.

. 'I'he plus 10 mesh material goes through a magnetic pulley type or drytype separator and the material going through the 10 'mesh screen andplus 20 mesh goes through a separate magnetic pulley separator. Thetails from these two magnetic separations go to waste and theconcentrates are shown as being returned 4to the preheater for furtherroasting-grinding treatparticular mesh is shown by way of illustrationand screens of other desirable mesh can be used.

The magneticseparators shown for the larger sizes of dry material are-ofrthe magnetic pulley or dry type; while the other magnetic -separatorsshown', applied to the wet material after hydraulic classification, arewet types of separators.

ment. The material passing through the 20' mesh screen is shown as goingthrough a hydraulic classier and as there being separated into coarse,medium and ne sizes which'go separately to Wet magnetic separators. Theheads of these three magnetic separators i'orm part of the concentrate.The tails are subjected to further magnetic separation in each case andthe tails from these further magnetic separations go to waste. The headsfrom these further magnetic separators may be returned as ,middlings.for treatment inthe master-grinder or may be combined as part of theconcentrate.

-It may or may not be necessary rto de-magnetize'the concentrate. Ifde-magnetization is desired a suitable de-magnetization treatment may beused, e. g., an alternating current coil. Any suitable method ofde-watering may be used if necessary. With lsome separators de-Watering`Where hydraulic classification is not used, and only dry screening isused for classification and sizing of lthe ore, dry types of magneticseparators can be employed.

The hydraulic classifier shown may bevof any suitable type which willseparate the material into a number of sizes, using either free settlingor hindered settling classifications. The ores may 4thus be separated,e. g., into a coarser size which is minus 20 and Aplus 40, a medium sizewhich is minus 20 and plus 60 and a finer' size which is minus 60.

The process is not dependent on fthe use of'any one type of magneticseparator but advantageously makes use of a suitable eld strength neticseparator of the coarse material from theA hydraulic classifier is shownas returning as middling to the preheater. The concentrate from thesecond magnetic separators for the medium and fine material m-ay eithergo to the concentrate or be returned, as indicated in dotted line asmiddlings to the preheater.

It will be noted that the particular number of sizes into which the oreis separated and the particular nature and number of magnetic separationtreatments can be varied to take full advantage of the diiferent sizesof material, including both coarser and finer sizes, present in the oreafter the combined master-grinder treatment.

While the ow sheet shows the combined operations with magneticseparation, for.which the material after the combined reducing andgrinding treatment is particularly adapted, other types of separation,such as wet methods or tabling methods, may be used.

The results obtained by -the combined roasting and grinding treatment of.the present invention will be illustrated by the following example ofthe treatment of a low grade oolitic hematite was crushed to minus 1Ainch, preheated to about 1050 F. and subjected to a combined reducingand grinding treatment in a ball mill type of apparatus with increase`in temperature to about 1200 F. and using coke oven gas as the reducingatmosphere, the time of treatment being about 25 minutes. 'I'he materiallost about 7% in Weight and showed 37.0% iron, 29% insoluble. 'I'hismaterial was cooled to atmospheric temperature in a reducingatmosphereand was `then separated by screening using 10, 20, 40, 60 and meshscreens.

The plus 10 and plus 20 sizes were subjected to dry magnetic separationand the middlings obtained were reground to minus 60 mesh and subjectedto Wet magnetic separation. The ner sizes were subjected separately towet magnetic separation. The nal concentrate obtained represented 62.4%of the roasted ore and contained 53.1% iron, 9.7% calcium oxide, 0.31%phosphorous, 0.08% manganese and 13.6% insoluble. The tails obtainedrepresented 34.7% of the weight of the roasted ore and contained 11.7%

iron and 48.3% insoluble.

While the invention has been described more particularly in connectionwith the treatment of low grade oolitic hematite ores, to which it isparticularly applicable, the invention in its broader aspects includesthe treatment of other low grade oxidized ores such as other low gradeoxide and carbonate ores,` etc. With carbonate ores the combinedroasting and' grinding treatment results in decomposition of thecarbonate's with elimination of' carbon dioxide and conversion of thecarbonatev to oxide: and, with a regulated reducing treatment combinedwith the grinding operation, the carbonate ore ls readily converted intoa' magnetic condition Well adapted for subsequent separation of magneticseparation.

We claim:

1. The method of concentrating low grade oxidized iron ores whichcomprises subjecting the ore while at a temperature varying from 900 F.to 1500 F. to a combined roasting and grinding treatment to effectgrinding and separation of the metal bearing material and gangue, saidgrinding being effected by breaking the ore under the impact of a hardbody to such fineness that it will substantially all pass through a 10-mesh screen, said roasting and temperature conditions being such as tocause the ore to break more edectively when subjected to impact at thetime of roasting, and subsequently subjecting the ore to a separationtreatment to eiect concentration of the ore and separation of ganguetherefrom.

2. The method of concentrating low grade oxidized irons ores whichcomprises subjecting the ore to a combined reducing and grindingtreatment at a temperature of about 900 to 1500 F. to effect grindingand separation of the metal bearing material and gangue while hot andsubjected to reducing conditions, the ore being ground to such iinenessthat it will substantially Y all pass through a lil-mesh screen andsubsequently subjecting the ore to a separation treatment to edectconcentration of the ore and separation of gangue therefrom.

3. The method of concentrating low grade oxidized iron ores whichcomprises subjecting the ore to a grinding treatment and alternatelysubjecting the ore to reducing and oxidizing conditions during suchgrinding treatment to effect separation of the metal bearing materialand gangue, said grinding, oxidizing and roasting being carried out atfrom 900 to 1500 F. to eiect a change in the structure of the orecausing it to break easily under the impact of a hard body, andsubsequently subjecting the ore to a separation treatment to effectconcentration of the ore and separation-of gangue therefrom.

4. The method of concentrating low grade oxidized iron ores whichcomprises subjecting the ore to a combined reducing and grindingtreatment at; a temperature varying from 900 to 1500 -F. to effectgrinding and separation of the metal bearing material and gangue whilehot and subjected to reducing conditions, the ore being ground to suchiineness that it will substantially -all pass through a 10-mesh screenand subsequently subjecting the ore to a separation treatantonio ment toedect concentration of the ore and separation of gangue therefrom, saidseparation treatment including magnetic separation.

5. The method of concentrating low grade oxi-v dized iron ore whichcomprises subjecting a preheated ore in such state of subdivision thatit will substantially all pass through a 3/4 inch opening to a combinedroasting and grinding treatment at a temperature within the range of 900F. to 1500 F to edect grinding and separation of the metal bearingmaterial and gangue, said grinding being eiected by breaking theparticles of ore under the impact of a hard body, and subsequentlysubjecting the ore to a separation treatment to eilect concentration ofthe ore and separation of gangue therefrom.

6. The method of concentrating low grade oxidized iron ore whichAcomprises preheating the crushed ore, subjecting the preheated ore to acombined reducing and grinding treatment at a temperature at about 900to 1500 F. to eiect grindingand separation of the metal bearing materialand gangue while hot and subjected to reducing condition,the ore beingground to such iineness that it will substantially all pass through a10-mesh screen, and subsequently subjecting the ore to'a separationtreatment to edect concentration of the ore and separation of ganguetherefrom.

7. The method of concentrating low grade oxidized iron ores whichcomprises subjecting the same to a combined roasting and grindingtreatment while at a temperature Within the range of 900 F. to 1500o F.to eect grinding of the ore and to eiect separation of metal bearingmaterial and gangue to produce a product having particles of varyingsizes, said grinding being effected by breaking the particles under theimpact of a hard body and continuing the treatment until a substantiallportion of the particles are in a pulverulent state, subjecting theresulting ore to a sizing treatment to separate particles of diierentsizes and separately subjecting the sized fractions of the ore to aseparation treatment to concentrate the ore and separate the ganguetherefrom.

8. The method of concentrating low grade hematite ores which comprisessubjecting t the ore in such state of subdivision that it will substantially all pass through a 3/4 inch opening to a combined reducingand grinding treatment at a temperature varying from 900 to 1500 F. toeffect grinding of the ore While hot and under reducing conditions andto produce a magnetic iron ore having particles of varying sizes, theore being ground to such nneness that it will substantially all lpassthrough a lll-mesh screen, subjecting Athe resulting ore to a sizingtreatment to separate particles of different sizes, and separatelysubjecting the sized fractions of the ore to a separation treatment toconcentrate the ore and separate the gangue therefrom, said separationtreatment including magnetic separation.

9. The method of concentrating low grade oxidized iron ores whichcomprises subjecting the ore to 'a preliminary crushing treatment toreduce the particles to such iineness that the ore will substantiallyall pass through a 3@ inch opening, preheating the crushed ore,subjecting the preheated ore to a combined reducing andgrinding-treatment at a temperature of about 1000n to 1500 F. by passingreducing gases into contact therewith while subjecting the ore togrinding by breaking the ore under the impact of a hard body to suchfl'neness that a substantial portion thereof is in a pulverulent state,cooling the ground ore under conditions to prevent oxidation, andsubjecting the reduced ore to a separation treatment to concentrate theore and remove gangue therefrom.

10. The method of concentrating low grade oolitic hematite ores whichcomprises subjecting the crushed ore to a preheating treatment,subjecting the preheated ore to a combined reduc` ing and grindingtreatment at a temperature of about 1000 to 1500 F. by passing reducinggases into contact therewith while subjecting the 'ore to grinding andto produce a magnetic iron ore product having particles of varyingsizes, the particles being suiciently fine that substantially all of theore will pass through a -mesh screen, cooling the resulting ore underconditions to prevent oxidation, subjecting the resulting ore to asizing treatment to separate fractions of different sizes, andseparately subjecting the size fractions to a separation treatment toconcentrate the ore and separate Vthe gangue therefrom, said separationtreatment including magnetic separation.

1l. The method of concentrating low grade oxidized iron ores whichcomprises subjecting the ore to a combined reducing and grindingtreatment to eiect grinding and separation of the metal bearing materialand gangue while at a temperature varying from 900 to 1500 F. andsubjected to reducing conditions, said grinding being effected bybreaking the ore under the impact of a hard body to such neness that itwill substantially all pass through a 10-mesh screen, and subsequentlysubjecting the ore to a separation 'treatment to effect concentration ofthe ore and separation of gangue therefrom, said separation treatmentincluding a magnetic separation with the magnet strength so adjusted asto elect separation of the more magnetic material from the less magneticmaterial.

12. The method of concentrating low grade oxidized iron ores whichcomprises subjecting the ore to a combined reducing and grindingtreatment to effect grinding and separation of themetal bearing materialand gangue While at a temperature varying from 900 to 1500 F. andsubjected to reducing conditions, said grinding being effected bybreaking the ore under the impact of a hard body to such iineness thatit will substantially all pass through a 10-mesh screen, andsubsequently subjecting the ore to a separation treatment to'efectconcentration of the ore and separation of gangue therefrom, saidseparation treatment including a series of magnetic separations ofadjusted magnet strength to effect separation of the more magnetic .andless magnetic materials from each other and from the non-magneticmaterial.

13. The method of concentrating low grade oxidized' iron ores whichcomprises subjecting the same to a combined reducing and grindingtreatment to effect grinding of the ore while at a temperature varyingfrom 900 to 1500 F. and to effect separation of metal bearing materialand gangue to produce a product having particles of varying sizes, saidgrinding being effected by breaking the ore under the impact of a hardbody to such neness that it Will substantially all pass through a 10meshscreen, subjecting the resulting ore to a sizing treatment to separateparticles of different sizes, and separately subjecting the sizedfractions of the ore to magnetic separation of adjusted magnet strengthto effect separation of the more magnetic and less magnetic materials.

14. Ihe method of concentrating low grade oxidized iron ores whichcomprises subjecting the same to a combined reducing and grindingtreatment to eiect grinding of the ore while at a temperature varyingfrom 900 to 1500 F. and to effect separation of metal bearing materialand gangue to produce a product having particles of varying sizes, saidgrinding being effected by breaking the ore under the impact of a hardbody to such fineness that it will substantially all pass through a10-rnesh screen, subjecting the resulting ore to a sizing treatment toseparate particles of different sizes, said sizing treatment including adry screening separation of sized fractions of the ore, and separatelysubjecting the resulting sized fractions to dry magnetic separation. Y

15. The method of concentrating low grade oxidized iron ores whichcomprises subjecting the same to a combined reducing and grindingtreatment to effect grinding of the ore while at a temperature varyingfrom 900 to 1500 F. and to effect separation of metal bearing materialand gangue to produce a product having particles of varying sizes, saidgrinding being effected by breaking the ore under the impact of a hardbody to such finess that it will substantially all passA through a10-mesh screen, subjecting the resulting ore to a sizing treatment toseparate particles of different sizes, said sizing treatment including aWet classification separation of sized fractions ofthe ore, andseparately subjecting the resulting sized fractions to wet magneticseparation.

LE ROY EDGAR SCHIFFMAN.

CLAUDE SIMS LAWSON.

JOSEPH THOMAS BLAKEMORE.

